CL-232 Lab Experiment FM-202 : Nature of Flow Staff TA’S Mr. Amit Shinde Munish Kumar Sharma Mr. B.G. Parab Laxman R. Bhosale

Objectives To visually observe laminar and turbulent flow patterns To determine the upper and lower critical Reynolds number Experimentally determine the friction factor and compare with model prediction

Schematic diagram

Theory Fluid flow in a pipe may be laminar or turbulent depending upon the conditions of flow. At low fluid velocities, the fluid moves without lateral mixing and without any eddies formation. The streamlines remain distinct from one another over the entire length (Laminar flow). At high fluid velocities, eddies form in the fluid under motion causing lateral mixing and formation of eddies. The flow is chaotic (Turbulent flow).

Reynolds no. Reynolds no. is used to characterize the flow: N Re = D v ρ/ μ Where D = dia of the pipe; v = avg. velocity of fluid; μ = dynamic viscosity For a pipe flow: N Re < 2100 (Laminar regime) 2100 < N Re < 4000 (Transition regime) N Re > 4000 (Turbulent regime) N Re, upper critical: flow behavior change Laminar to Turbulent N Re, lower critical: flow behavior change Turbulent to Laminar

Friction factor Friction factor (f) is defined as the ratio of wall shear stress to the product of the density and velocity head. It is given by the following relation: f = ΔP g c D/ 2 L ρ V 2 Where ΔP = pressure drop across pipe; L = length of pipe; D = dia of pipe; V = average velocity of fluid; ρ = fluid density Model (Theoretical) predictions of friction factor: f = 16/ N Re (Laminar flow) f = N Re -0.2 ( < N Re < 10 6 ) f = (0.125 / N Re 0.32 ) (3000 < N Re < 3×10 6 )

Observations Measure h1 (pressure head in Tank-1) and h2 (pressure head in Tank-2) for laminar flow. Start increasing the flow rate through discharge valve and take h1 and h2 again and measure the flow rate. Take atleast 10 such readings and one extra reading at maximum flow rate. Now start decreasing the flow and repeat the above step again. The flow will shift from turbulent to laminar once again. Calculate the Reynolds no. for every reading and characterize the flow. Report N Re, upper critical and N Re, lower critical values. Calculate the friction factor experimentally and compare it with the model predictions on a log-log plot.